1. Field of the Invention
The present invention relates to a hydraulic circuit for a crane in which a boom hoisting motor circuit and a wind-up motor circuit are connected in series to one and the same hydraulic source.
2. Description of the Related Art
In a case of a normal crawler crane, there are provided winches 1,2 and 3 which are a boom hoisting winch, a main winch and an auxiliary winch, respectively, as shown in FIG. 3. A main jib (boom) 4 is hoisted by the winch for a boom hoisting 1. A main hook 5 suspended from the extreme end of the main jib 4 is moved up and down by the main winch 2. An auxiliary hook 7 suspended from an auxiliary jib 6 mounted on the extreme end of the main jib is moved up and down by the auxiliary winch 3.
In a case of a luffing crane, an auxiliary jib 9 is mounted on the extreme end of a tower type main jib 8, as shown in FIG. 4. A main hook 5 is suspended from the extreme end of the auxiliary jib 9. The auxiliary jib 9 is hoisted by the auxiliary winch 3.
Operations (rotational operation is omitted in explanation here) including travel motion in these cranes are carried out by a hydraulic motor as a driving source. As hydraulic circuits, there are provided a main winding motor circuit, an auxiliary winding motor circuit, a boom hoisting motor circuit, and left and right traveling motor circuits.
A combination of a hydraulic source and an actuator is normally divided, as shown in FIG. 5, into a first actuator group A driven by a first hydraulic source 10 such as hydraulic pump and a second actuator group B driven by a second hydraulic source 11.
A left traveling motor circuit 12, a boom hoisting motor circuit 13, and an auxiliary winding motor circuit 14 belong to the group A. A right traveling motor circuit 15 and a main winding motor circuit 16 belong to the group B.
It is constituted such that in both the groups A and B, the respective motor circuits are connected in series between the hydraulic sources 10, 11 and a tank T, and can be operated either individually or simultaneously.
According to the hydraulic circuit constitution as described above, in the composite operation in which not less than two motor circuits are operated simultaneously, when both the motor circuits belong to the same group, there occurs the following problem.
In a case where the boom hoisting motor circuit 13 and the auxiliary winding motor circuit 14 are operated simultaneously, for example, in a case where a hanging article is moved up and down by the auxiliary hook 7 while hoisting the jib 4 shown in FIG. 3, pressure interference occurs between the circuits 13 and 14. Therefore, the respective operations fail to be carried out smoothly. In a case where the sum of pressure of both the circuits 13, 14 is high, a relief valve in the upstream circuit acts to relieve oil, thus resulting in an inconvenience that no operation can be carried out.
As shown in FIG. 6, a countermeasure is taken into consideration in which the boom hoisting motor circuit 13 is separated from the group A, and a third driving source 17 exclusive use for the circuit 13 is added. In this case, there poses a problem that an increase in cost and an increase in installation space are brought fourth due to further installation of the hydraulic source 17 and the increase in pipes and so on resulting therefrom.